Formation and dynamics of exciton pairs in solid argon probed by electron-stimulated ion desorption

Electron-stimulated desorption of Ar⁺, Ar₂⁺, Ar²⁺, and Kr⁺ ions from solid Ar and Kr was studied for the electron energy range from 10 to 120 eV. For Ar⁺ and Ar₂⁺ excitation resonances with onsets at 24.2, 25.4, 34, and 50 eV have been found. The two lowest thresholds cannot be explained by excitations of single Ar atoms. They are interpreted as pairs of interacting surface and bulk excitions, respectively, on neighboring atoms. The bulk species can diffuse over more than 100 layers. Novel conclusions about the desorption mechanism can be derived.